The invention relates generally to non-floating fluid level sensors, and more particularly to electrical systems for sensing and controlling fluid levels in containers.
Electrically resistive fluid level sensors are known generally for measuring conductive and partially conductive fluid levels and provide many advantages over floating mechanical sensors, including the substantial elimination of corrosion susceptible parts, reduced cost, and improved accuracy and reliability.
The referenced application Ser. No. 09/090,439 entitled xe2x80x9cResistive Fluid Level Sensing and Control Systemxe2x80x9d discloses fluid level sensors comprising generally a pair of carbon or polymeric resistive film elements disposed in a container, for example in a washing machine basin. The conductive or partially conductive fluid in the container provides a relatively low resistance, or short circuit, path between the resistive elements, thus forming a series connection therebetween. The resistance of the resistive elements varies continuously in proportion to the changing fluid level in the container. A corresponding change in a voltage output measured across the series resistive elements is indicative of the fluid level in the container, and in the exemplary washing machine application the output voltage is used to control the supply of fluid thereto. See also U.S. Pat. No. 5,083,460 entitled xe2x80x9cLevel Sensorxe2x80x9d.
U.S. Pat. No. 4,169,377 entitled xe2x80x9cQuantity Sensing System For A Containerxe2x80x9d discloses a level sensing system having a pair of series connected resistive elements disposed in a flowable material so that the resistance thereof varies discretely in some proportion to the changing material level. The resistive elements each include a resistive strip that is electrically isolated from the flowable material. Each strip has a plurality of electrodes disposed thereon in spaced apart relation and in electrical contact with the flowable material, thus providing discrete changes in the resistance of the resistive elements with the changing material level.
U.S. Pat. No. 5,626,053 entitled xe2x80x9cFloatless Gauge With Resistive/Conductive Polymerxe2x80x9d discloses a single elongate resistive member disposed into an electrically grounded fluid tank. The resistive member has a non-uniform cross-section along its vertical length corresponding to variations in the cross-section of the tank to compensate for variations in the distance between the resistive element and the electrically grounded tank side wall.
The present invention is drawn toward advancements in the art of fluid level sensing, and more particularly to resistive fluid level sensors and systems.
An object of the present invention is to provide novel resistive fluid level sensors and systems that are economical and that overcome problems in the art.
Another object of the invention is to provide novel resistive fluid level sensors and systems that are accurate and reliable.
Another object of the invention is to provide novel resistive fluid level sensors and systems that are fail safe.
It is also an object of the invention to provide novel resistive fluid level sensors and systems that sense changing fluid levels continuously.
Another object of the invention is to provide novel resistive fluid level sensors and systems that sense changing fluid levels discretely.
A further object of the invention is to provide novel resistive fluid level sensors and systems for sensing fluid levels in containers, for example washing machine basins, and for terminating the supply of fluid thereto when the fluid level therein reaches a specified level.
Yet another object of the invention is to provide novel resistive fluid level sensors and systems for sensing fluid levels in containers that are electrically grounded, for example some washing machine basins.
A more particular object of the invention is to provide novel fluid level sensing systems comprising generally a resistive element having an upper end portion disposed in an upper portion of a container and a lower end portion disposed in a lower portion of the container, wherein the electrical resistance per unit length of the resistive element varies between the upper and the lower portions of the container. The system also comprises a conductive or partially conductive strip having substantially the same length as the resistive element. The strip is disposed in the container generally parallel to the resistive element and at approximately the same level in the container as the resistive element.
Another more particular object of the invention is to provide novel fluid level sensing systems comprising generally a resistive element having an upper end portion disposed in an upper portion of a container and a lower end portion disposed in a lower portion of the container, wherein an electrical resistance per unit length of the resistive element increases toward the lower portion of the container and decreases toward the upper portion thereof. The system also comprises a conductive or partially conductive strip having substantially the same length as the resistive element. The strip is disposed in the container generally parallel to the resistive element and at approximately the same level thereof in the container.
Yet another object of the invention is to provide novel fluid level sensing resistive elements comprising generally an electrically insulated semi-conductive film strip comprising a plurality of discrete strip portions deposited onto a non-conductive substrate. Each of the discrete strip portions of the resistive element has a corresponding width dimension, wherein the width dimensions toward a first end portion of the non-conductive substrate are wider than the width dimensions toward an opposite second end portion thereof. A plurality of electrodes are disposed in spaced apart relation on the non-conductive substrate and coupled to a corresponding one of the discrete strip portions of the resistive element.
Still another object of the invention is to provide novel fluid level sensing resistive elements comprising generally an electrically insulated semi-conductive film strip deposited onto a non-conductive substrate, the semi-conductive film strip having a width dimension with a continuously narrowing taper between first and second end portions thereof, the first end portion of the semi-conductive film strip having a wider width dimension than the second end portion thereof.